Bare quantum dots superlattice photonic devices

Abstract

Manipulation of the passivation ligands of colloidal quantum dots and use in QD electronics. A multi-step electrostatic process is described which creates bare QDs, followed by the formation of QD superlattice via electric and thermal stimulus. Colloidal QDs with original long ligands (i.e. oleic acid) are atomized, and loaded into a special designed tank to be washed, followed by another atomization step before entering the doping station. The final step is the deposition of bare QDs onto substrate and growth of QD superlattice. The method permits the formation of various photonic devices, such as single junction and tandem solar cells based on bare QD superlattice, photodetectors, and LEDs. The devices include a piezoelectric substrate with an electrode, and at least one layer of bare quantum dots comprising group IV-VI elements on the electrode, where the bare quantum dots have been stripped of outer-layer ligands.

Description

FIELD OF INVENTION[0001]This invention relates to the quantum dot films. Specifically, the invention provides for quantum dot ligand manipulation, and formation of superlattice film by multi-step electrostatic deposition technique.BACKGROUND OF THE INVENTION[0002]More energy from the sun strikes the Earth in one hour than all the energy consumed on the planet in one year, yet solar electricity accounts for less than 0.02% of all electricity produced worldwide. The enormous gap between the potential of solar energy and its use is due, in part, to the cost / conversion capacity. The development of third generation solar cells (high efficiency plus low cost) is of paramount importance to both humanity and nature.[0003]Solution-processability has been recognized as a feasible solution to cost issues, and novel mechanisms such as carrier multiplication a possible route to achieve higher efficiency levels. In both these aspects, there is potential in colloidal infrared quantum dots, such as...

AI Technical Summary

Benefits of technology

The patent text discusses the importance of the arrangement of quantum dots (QDs) in device performance. Highly ordered QD arrays have been shown to have better trap density and carrier mobility, resulting in better device performance. The text also mentions the formation of a "miniband" in Si QD solar cells, which can improve band-like transport behaviors. The text describes various methods for introducing perturbation to guide QD assembly, such as solvent vapor processing, drop-casting, spin-coating, and electrostatic layer-by-layer deposition. The text concludes by stating that the ligand surface coverage determines the shape of QDs, which affects the symmetry of the QD superlattice.

Problems solved by technology

This is in part owing to the inherent complexity of QD self-assembly process.

However, none of these methods are for bare QDs, and the drastic change in surface conditions could bring in completely different results on QD superlattice properties.

Furthermore, even for ligand-QD superlattice, existing results are mainly on the structural study, and the systematic probe on optical and transport properties of QD superlattice, and correlation between device performances are still missing.

In the case of QD solar cell, another issue is the device design, which includes the photoactive layer and device architecture.

Through many futile attempts to drastically improve the efficiency of hybrid solar cell-photoactive layer consisting of organic polymer as electron donor and inorganic QDs as electron acceptor, this design rule has turned out to be intrinsically defective due mainly to the large mismatch of bandgaps, and inefficient charge transfer between donor and acceptor (Moulè, et al., Hybrid solar cells: basic principles and the role of ligands, J. Mater. Chem., 2012, 22, 2351).

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